Aquatic Lash

While a Black Sapphire is fastened to the circlet, one of the spectral weapons takes the form of a Trident imbued by the Elemental Plane of Water. If you hit a creature with this weapon and you deal damage to it, you can reduce its Speed by 10 feet until the start of your next turn and it takes an additional 1d8 Cold damage, or 2d8 Cold damage if the creature is an Elemental. If the creature is hit more than once by weapons that have the Slow property, the Speed reduction doesn't exceed 10 feet.